Northrop Grumman E-2A/B/C/D Hawkeye

The harsh lesson of what can happen when a naval task force gets involved in a shooting war without an effective Airborne Early Warning (AEW) system was drawn into sharp focus during the Falklands War of 1982. In this conflict, played out in the unforgiving climate of the South Atlantic, the inability of the RAF to provide AEW cover with their antiquated Avro Shackleton AEW Mk2 aircraft from a nearby land base as planned, left the Royal Navy (RN) taskforce dangerously exposed and had a direct impact when HMS Sheffield and the Atlantic Conveyer were lost to attacks by low-flying by Super Etendard aircraft launching Exocet missiles.

As far back as 1942 the US Navy had recognised the treat posed by low-flying aircraft approaching a naval task force underneath radar cover, which is limited to a radar horizon of around 30 miles, giving little warning of an impending attack. This requirement led to Admiral Ernest J King, the US Navy C-in-C of the US Navy, to issue a request to Dr Vannevar Bush, the director of the Office of Scientific Research and Development (ORSD) to develop a radar-relay system which would allow the exchange of radar information between ships. The radar-relay project, NA-112 was established in June 1942, with D Division of the Massachusetts Institute of Technology – Radiation Laboratory (MIT-RL) doing much of the initial work, but made slow progress. In early 1944, following a review of the progress of NA-112, it was decided to change the focus of the project away from a radar-relay system to the development of an AEW system, renamed Project NA-178, with the MIT-RL again leading the work. In Feb 1945 the development programme was renamed Project Cadillac, after Cadillac Mountain in Maine where much of the early testing was conducted.

The AEW radar developed under Project Cadillac was known as the APS-20 and during 1944 it was mounted in a General Motors TBM Avenger and as the TBM-3W this became the first AEW aircraft to undergo testing. The APS-20 radar was one of the great scientific developments of WW2, but was still undergoing testing when the war ended. The radar operated in the S-Band and featured a 8ft by 3ft parabolic dish antenna mounted in a plastic fairing underneath the aircraft, giving 360 degree coverage. The radar system also incorporated various highly advanced innovations including an Identification Friend or Foe (IFF) as well as a transmitter that relayed both the radar picture and the IFF information to receiver stations onboard adjacent ships. The relay transmission system was called ‘Bellhop’, but it was a long time before it operated effectively. Two operators worked the radar and ‘Bellhop’ system, but excessive clutter, the lack of an automatic tracking system and symbology were significant weaknesses – radar returns were manually tracked by drawing marks with a chinagraph pencil on the screen itself, significantly limiting the capacity of the operators.

Under a programme known as Cadillac II, the Navy also fitted the APS-20 radar system onto the B-17G aircraft, giving it the designation PB-1W, but although this aircraft had much greater endurance and could carry a larger crew, it could not operate from a carrier deck and entered operational service after the war in the Pacific was over. The US Navy also investigated the benefits of mounting the APS-20 on an airship and although this platform could offer much greater endurance, it still possessed many of the weakness of the PB-1W. Eventually a number of carrier capable Grumman AF-2W Guardians were equipped with the APS-20 radar, but the US Navy seemed intent on using the AEW capabilities of the aircraft in other roles and mainly employed the aircraft in partnership with an anti-submarine version of the same aircraft, known as the AF-2S, to located and destroy enemy submarines.

The US Navy then decided to replace their GM TBM-3W Avengers by modifying a version of the Douglas Skyraider into an AEW aircraft by again fitting it with the APS-20 radar and associated systems. Eventually 29 of the Douglas AD-3W Skyraiders were produced between 1948-9 and these were followed by 168 versions of the AD-4W Skyraider produced between 1950-1. The US also sold 50 versions of the AD-4W to the Royal Navy. The final version of this aircraft was the AD-5W, which incorporated many changes learnt from operating the earlier versions, in total 218 examples were built. All AEW Skyraiders had a ventral radome housing the APS-20 radar and generally operated with a single pilot and two crewmen, although some aircraft also carried a technician as well. However, the common thread in all these aircraft was the APS-20 radar, which suffered badly from clutter, lacked an automatic tracking system and associated symbology, that significant weaknesses which by the mid to late 1950’s needed urgent attention.

The only solution was a purpose-built AEW aircraft with a completely new AEW radar and associated systems. In 1955 the US Navy Bureau of Aeronautics issued a requirement for a new carrier based AEW and Air Intercept Control (AIC) aircraft, which was won by Grumman. However, the Navy accepted that there would be a long delay before the many technical problems with the winning design could be overcome; however, because a replacement AEW aircraft was urgently required, an interim design was accepted. The result was the Grumman E-1B Tracer, nicknamed the ‘Willie Fudd’, a modified version of the Grumman Tracker. This aircraft was fitted with the APS-82 Hazeltine S-Band radar mounted above the fuselage in a teardrop shaped radome. This was the same radar that had been used in the WV-2E Super Constellation and, although it was a great improvement over the APS-20 radar, the supporting systems still lacked data symbology, automatic tracking and only had a limited height finding capability. Nevertheless, the data links were vast improvement on the old Bellhop system. The E-1B was crewed by two pilots and two controllers and usually operated between 5,000 -7,000ft. The aircraft remained in service for 16 years from 1962 to 1978 until it was replaced by the E-2A – so much for an interim design!

The new design that caused all the delay was the Grumman E-2A Hawkeye. This was the first time that an aircraft had been designed from the outset solely for AEW operations, rather than being an adaptation of an existing design. Nevertheless, the problems facing the design engineers at Grumman were immense and were compounded by having to constrain the design to enable the aircraft to operate from the older ‘modified Essex class’ carriers. These ‘smaller’ carriers were all built during WW2 and later modified to allow them to operate jet aircraft. Consequently, various height, weight and length restrictions had to be factored into the E-2A design, resulting in some handling characteristics which were less than ideal. In the event the E-2A only operated from the modified Essex class for a few years before the ships were scrapped; in retrospect the design would have benefited considerably if this requirement had been lifted from the outset and the restrictions had never been imposed.

The Grumman design engineers faced enormous difficulties in building a carrier based aircraft that could carry a crew of two pilots and three controllers, as well as the radar and associated systems, within the various design parameters that had been set and the end result was by any standards an extraordinary accomplishment and one that has never been successfully completed by any other country. The new B-band AN/APS-96 radar designed by General Electric was carried in a rotating rotodome mounted above the fuselage. The lower frequency and high pulse repetition interval of the radar gave it greater range, far more power, vastly better detection capability and made it much less affected by weather and clutter. Powered by two powerful Allison T56-A-8 turboprops, the aircraft was designed to operate between 25,000 to 30,000ft giving it a radar range in excess of 200nms and enabling it to detect aircraft operating up to 100,000ft. Computer systems would automatically track targets and generate speed and heading information for the controllers. However, although the E-2A Hawkeye first flew on 29 Apr 1961 and entered service with VAW-11 in Jan 1964, major problems lay ahead and it would be many, many years before a modern and reliable AEW system would be in operational service.

By 1965 the major development problems were still delaying the E-2A Hawkeye got so bad that the aircraft was actually cancelled after 59 aircraft had already been built. Particular difficulties were being experienced because of inadequate cooling in the closely packed avionics department – a problem that has bedevilled many AEW designs. Early computer and complex avionics systems generated considerable heat and, if this wasn’t channelled away effectively, caused serious problems, eventually resulting in some failure or other. These system failures continued long after the aircraft entered service and at one point reliability got so bad that the entire fleet of aircraft was grounded. Eventually in 1965, after Navy officials had been forced to explain to Congress why four production contracts had been signed before the extensive avionics testing had been completed, action was taken. The unreliable rotary drum computer was replaced by a Litton L-304 digital computer and various other avionic systems were replaced – the upgraded aircraft were designated E-2Bs. In total 49 of the 59 E-2As were upgraded to E-2B standard and these aircraft replaced the E-1B Tracers in the various US Navy AEW squadrons and it was the E-2B that was to set a new standard for carrier-based AEW aircraft.

However, although the upgraded E-2B was a vast improvement on the unreliable E-2A, the US Navy knew the design had much greater capability and still had yet to achieve the performance and reliability parameters set out in the original design back in 1957. In Apr 1968 it instigated the next reliability improvement programme. In addition, now that the capabilities of the aircraft were starting to be realised, more were needed and, as well as the 49 E-2Bs that would be upgraded, another 28 new E-2Cs were ordered. The improvements in the new and upgraded aircraft were concentrated in the radar and computer performance. The new General Electric AN/APS-120 UHF radar was fitted to all the aircraft and this incorporated an Airborne Moving Target Indicator (AMTI), finally giving the aircraft an overland capability and included a linked AN/APS-72 or 76 IFF. Additional Litton L-304 computers were also fitted to increase the signal processing capability. Of probably even greater significance was the installation in the nose of the Litton AN/ALR-59 Passive Detection System (PDS) Electronic Support Measures (ESM) which enabled the aircraft to detect other radar or radio systems at very long ranges, before they had any possibility of detecting the Hawkeye. Further interceptions by the PDS allowed the source of the signal to be triangulated, revealing its location. The problem associated with increased heat generated by the additional electrical systems was solved by adding an additional air-scoop housing a vapour cycle cooling system condenser. To compensate for the increased weight, the engines were replaced by more powerful T56-A-425 turboprops. When it was finally introduced into service in 1974, the E-2C possessed a unique capability and was by some distance the best AEW system in the world; at last all the delays and problems experienced during the lengthy development programme were beginning to pay off.

However capable the early E-2C was everyone associated with the programme knew that the E-2C could be improved and were determined to continue development of the system. To this end, throughout its service life the E-2C has been almost continually upgraded. In the 1970s the first upgrade added the Total Radiation Aperture Control-Antenna (TRAC-A) and the General Electric (later Lockheed Martin) AN/APS0138 radar. The ESM PDS was replaced with the Litton AN/ALR-73 and addition Rockwell-Collins AN/ARC-182 Have Quick HF/VHF/UHF secure radios replaced the communications system, reducing the possibility of electronic jamming. The computer memory of these aircraft was increased to 16K, a pathetic amount in 2006, but a really large amount at the time. These upgraded E-2Cs could track up to 300 targets and were known as Group 0 aircraft – they began arriving on carriers in the 1980s, serving until the 1990s when they were replaced by Group 2 aircraft.

In the next production run between 1988 and 1991 saw 18 aircraft built to the Group 1 standard. The AN/APS-139 radar was fitted and this fed a Standard Central Air Data Computer (SCADC), linked to an improved version of the Litton L-304 computer, increased by 400% the number of targets that could be tracked. Additional cooling capacity was added to dissipate the extra heat generated by the new electrical systems and more powerful Allison T-56-A-427 turboprops were installed. A total of 18 Group 1 aircraft were built with the first entering service on 8 Aug 81 - this version was only flown by the Atlantic fleet squadrons.

The Group 2 configuration includes the AN/APS-145 Advanced Radar Processing System (ARPS) housed inside a Randtron AN/APA-171 rotodome antenna group alongside a Hazeltine AN/APX-76 IFF interrogator set. This new system allowed simultaneous detection and tracking of surface and airborne targets and offered increased resistance to jamming. The Combat Information Centre (CIC) in the cabin was also upgraded – the old circular monochrome display screens were replaced by three colour 11in x 11in Enhanced Main Display Unit (EMDU) tactical display screens which could be accessed by either buttons or a lightpen - additional data was displayed on a smaller Auxiliary Display Unit (ADU). Inside the CIC the Combat Information Centre Officer (CICO) is seated in the middle console, on his right is the Radar Officer (RO) (always the most junior member of the CIC team) and on his left is the Air Control Officer (ACO). All three face the consoles mounted on the port side of the aircraft on seats that can swivel to face forward for take-off and landing – no ejection seats are fitted for any of the crew and parachutes are not usually carried. The CICO, who is always the Mission Commander, chooses the parameters of the flight and assigns tasks within the CIC. All three controllers monitor the data from the various systems. However, the ACO is primarily responsible for establishing links to aircraft and other units via the Have Quick radios and datalink systems and is equipped with a Multi Function Control Display Unit (MFCDU) as well as an EMDU. A total of 50 Group 2 aircraft were eventually delivered, with 12 being upgraded Group 1 aircraft. This new version entered service in June 1992 and has served with the Pacific and Atlantic Fleet squadrons.

At one point it was hoped that the Common Support Aircraft (CSA) would replace the E-2C, as well as the Lockheed S-3B Viking ASW and tanker aircraft, the Lockheed ES-3A ELINT platform and the Grumman C-2A Greyhound Carrier On-board Delivery (COD) aircraft. However, the CSA was cancelled in the late 1990s, allowing plans for the upgrade of the E-2C to continue. By 1997 the US Navy intended that all the front-line squadrons would be equipped with a total of 75 Group 2 aircraft. However, when Grumman merged with Northrop in 1994 plans began to be finalised for the next upgrade, known as the Group 2 Plus, which eventually became known as the Hawkeye 2000. By this time computer technology had advanced enormously and the Litton L-304 mission computer was really beginning to show its age. In its place was installed the smaller, much faster and considerably lighter Raytheon Model 904 mission computer, with an open architecture system that made future upgrades much easier. A Removable Media Cartridge (RMC) allowed mission related data to be loaded before take-off and then extracted after landing for review. The EMDU and ADU units were replaced by a 21in x 21in Advanced Control Indicator Set (ACIS), accessed via a trackball rather than a lightpen. The old ESM was replaced by the Lockheed Martin AN/AQL-217 system, giving increased coverage and the ability to classify more emitters. The additional heat generated necessitated the installation of a new Allied Signal vapour cycle cooling system.

Probably the most significant new system installed on the Hawkeye 2000 is the Raytheon Cooperative Engagement Capability (CEC) housed in a bulge underneath the centre of fuselage. The CEC is a system which allows warships and the E-2C to share theatre air defence data, across multiple platforms, via a C-band wideband data network. The CEC provides warships with over-the-horizon surveillance giving them much greater time to respond to an emerging threat. Housed in the under-fuselage bulge is the AN/USG-3 Common Airborne Set (CAS), consisting of a Digital Distribution System (DDS) and the 54in electrically steerable circular End Fire Array (EFA) antenna. To ensure the benefits of the CEC are not restricted by connectivity problems, an AN/ARC-210 SATCOM was also installed with the antenna housed in a distinctive circular bulge in the middle of the rotodome. However, not all Hawkeye 2000s will carry the CEC and to date only 17 aircraft have been fitted with this desirable system.

The other really noticeable change in the Hawkeye 2000 is the replacement of the old four-bladed propellers, which were no longer in production, with eight-bladed Hamilton Standard NP2000 composite propellers. The new propellers are more efficient, give less vibration and are quieter and also allow individual blades to be changed. The first Hawkeye 2000, which still retained the E-2C designation, was delivered in Oct 01 and the new variant reached initial operating capability in 2003. Original planes called for the E-2C Group 2 aircraft to be upgraded to the Hawkeye 2000 standard; however, this was later replaced by a plan for a multi-year production of new Hawkeye 2000 aircraft, with the factory at Northrop Grumman’s plant at St Augustine, Florida producing four aircraft per year. To reflect the new capabilities of these aircraft, the US Navy AEW squadrons are now known as Battle Management Command and Control Squadrons.

As before the planning for the next generation of Hawkeye, known as the Advanced Hawkeye or E-3D is already well under way. The E-3D will introduced some new stronger airframe structures, machined from single blocks of lightweight aluminium or made of composite materials, enabling the aircraft to operate at higher weights. The new APY-9 radar, combining mechanical rotation and electronic scanning, will be fitted that will allow various new scanning modes, including a purely electronic scan where the rotodome is held constant, focusing more energy on the target. The greater power of the radar will increase the volume of airspace covered by some 250%. External difference will include the replacement of the ‘dunces cap’ of AN/ARC-210 SATCOM with a flush fitting unit. The CEC bulge on the underside of the aircraft will be joined by a ‘horse collar’ fairing housing a trailing wire for some new communication or detection system. As with every upgrade to the Hawkeye, the cooling system will be upgrade and the capacity increased.

Inside the CIC new larger displays will be installed and additional communications facilities will be added. These include a new computer system which will act like a ‘server in the sky’ for other aircraft, including UAVs, enabling much greater network connectivity. In the cockpit the old 1960s style analogue instruments will be replaced by three multi-functional 17in flat screen displays, enabling the co-pilot to act as a fourth operator during the mission. An in-flight refuelling probe will be added at a later date, once issues concerning the effect the jet efflux from the Boeing F/A-18E Super Hornet on the rotodome have been resolved. Until 23 Sep 2005 the US Navy Hawkeye’s were organised into east and west coast wings, supporting the Atlantic and Pacific fleets respectively. However, the east coast wing has now been disestablished and all aircraft are now organised into a single wing based at Point Mugu, California. Construction of the first E-2D began in Apr 05 and the first flight is expected to take place in Aug 07. Initial operating capability is scheduled for 2011 and under current plans a total of 75 aircraft will be built, equipping 12 squadrons with four aircraft each. Currently a four aircraft detachment equips each Carrier Battle Group, although the greater use these highly capable aircraft will be put through have led some calls for the detachment size to be increased to six aircraft.

The success of the E-2 Hawkeye led to many other countries wanting to acquire an AEW capability and they watched the development of the aircraft carefully. However, the USA has, quite rightly, always been very careful which country it allows to acquire any new advanced military capability, furthermore, it wasn’t until the appearance of the E-2C that the system was actually sufficiently robust to attract an export order. The Israeli Air Force (IAF) was the first export customer and received four E-2C Group 0 aircraft between 1977 and 1978 where they were known in Hebrew as the ‘Daya’ or Kite and given the designations 941, 942, 944 and 946. The IAF locally fitted in-flight refuelling probes to two of these aircraft to extend their time on-station. These aircraft played a major part in the Beka Valley battles of 1982 where, in a carefully co-ordinated attack, the Syrian Air Force (SAF) were drawn into the air and destroyed en-mass by IAF F-15s and F-16s guided onto their targets by the Hawkeye’s. The effect of this utter annihilation of the cream of the SAF, where a total of 85 aircraft were eventually lost, was so traumatic that they have never again attempted to challenge the IAF.

However, the IAF E-2Cs were still optimised for over-sea, rather than over-land operations and although they were later modified by some locally produced avionics to improve their performance, they still lacked many of the capabilities the IAF wanted. To overcome these deficiencies the Israeli defence industry was developing the Phalcon AEW&C system and, when this became operational in 1994, the four E-2Cs were retired and became surplus to requirements.

In 2003 three of these aircraft were advertised for sale in Flight magazine and were subsequently sold to Mexico, supposedly at a ‘knock-down’ price and came complete with a comprehensive spares package, but without the two in-flight refuelling probes, which were removed. After refurbishment by the Bedek Division of Israeli Aircraft Industries (IAI), the three aircraft, 941, 942 and 946 were then delivered to the Mexican Navy, with the final aircraft arriving in Nov 2004. One IAF E-2C, 944, was retained for display at the IAF Museum at Hatzerim. The three Mexican E-2Cs are operated by the Mexican Navy’s Primer Escuadron Aeronaval Alerta Temprana y Reconocimiento (PRIMESCATREC), the 1st Naval Early Warning Squadron, based at Tapachula, where they are mainly used for maritime surveillance duties, combating drug trafficking and protecting off-shore oil installations.

Japan was the next customer acquiring eight E-2C Group 0 aircraft between 1982 – 1985, followed by five more between 1992-3. All the aircraft are operated by 601 Hikotai, Keikai Kokutai (AEW Air Group) located at Misawa in northern Honshu. Japan originally planned to upgrade these aircraft to Group 2 standard, but instead opted up upgrade all 13 aircraft to the Hawkeye 2000 standard in a rolling programme, with the first refurbished aircraft flying on 14 Jul 04.

In 1987, following Japan’s example, Singapore acquired four Group 0 Hawkeye’s. The aircraft have been continually upgraded throughout their service and are currently up to Hawkeye 2000 standard – all four Hawkeye’s are operated by the 111th Squadron based at Tengah.

Egypt was the next customer for the Hawkeye when they took delivery of five Group 0 aircraft in 1986, followed by one other Group 2 aircraft in 1993 - all the aircraft are operated by the 222 Fighter Regiment located at Almaza/Cairo West airbase. The six aircraft are in the process of being upgraded to Hawkeye 2000 standard, with the final aircraft being returned to Egypt in Apr 2007.

In 1995 Taiwan took delivery of four new built E-2C Group 2 aircraft which are operated by 78 Squadron based at Pingtung North. Two further Hawkeye 2000’s were delivered between 2004-5. All four of the Group 2 aircraft will be upgraded to Hawkeye 2000 standard between 2006-7.

Given the general French distaste for all things American, perhaps the most surprising customer for the Hawkeye was the French Navy. The simple fact was that the French government were not about to risk the huge expenditure and immense technical difficulties involved in attempting to build their own carrier based AEW aircraft and opted instead to grit their teeth and by American – something they have repeated with the E-3F Sentry. The first two French E-2C’s, built to Group 2 standard, were delivered in Dec 1998 and Apr 1999 respectively. A third Hawkeye 2000 standard aircraft was delivered in 2004. Plans are underway to upgrade the two Group 2 aircraft to Hawkeye 2000 standard and a fourth E-2C Hawkeye 2000 has also been ordered. All the aircraft are operated by 4 Flottille from the aircraft carrier Charles de Gaulle and when not at sea are based at Lann-Bihoue.

The next country likely to operate the Hawkeye will probably be the United Arab Emirates Air Force. They are currently negotiating to buy five former US Navy E-2Cs that are currently in storage at Davis-Monthan Air Base in Arizona. The aircraft will be refurbished to Hawkeye 2000 standard and may also be fitted with in-flight refuelling probes. If the order goes ahead, subject to some concerns about technology transfer, deliveries would take place between 2006 and 2008.

India, Pakistan and Malaysia have also examined the possibility of operating E-2C Hawkeye’s. However, instead India has ordered the Phalcon system fitted to a number of IL-76 Candid aircraft, Pakistan has ordered an unspecified number of SAAB 2000 aircraft fitted with the Eyrie radar and Malaysia appear likely to opt for the Phalcon system fitted onto a number of Gulfstream V aircraft or a number of Embraer EMB-145 AEW&C aircraft.

The RN are currently studying various AEW&C options, to replace their Sea King ASaC.7 helicopters, under the Maritime Airborne Surveillance and Control (MASC) programme, hopefully to operate from the highly controversial two large carriers planned to replace the three Invincible class carriers. Much as the RN would love to operate the E-2D from these carriers, it’s very unlikely they will be fitted with catapults or arrestor wires, making the operation of fixed wing AEW aircraft impossible. Allowing the RN to operate the latest standard of Hawkeye, with the increased ease of intra-operability with US forces that would bring, from the decks of the new carriers would make considerable sense. However, desirable military requirements rarely emerge victorious in a battle with the Treasury ‘bean-counters’ and even if the two carriers are built, which is by no means certain, I expect they will end up operating Merlin ASaC helicopters alongside Joint Strike Fighters.

Back in the late 1960’s, when the E-2A was suffering all its development and reliability problems, few would have imagined how developed versions of this aircraft have gone on to prove themselves in a wide variety of roles and have become an indispensable asset to US and other forces worldwide. From being simply an AEW aircraft the Hawkeye has, following its various upgrades, evolved into an aircraft that can perform the Airborne Battlespace Management (ABM) mission, utilising its highly advanced radar and communications systems. Put simply, wherever the Hawkeye operates, it becomes probably the most essential node in a network-centric operations, linking aircraft, ships and command centres, ensuring that information on potential threats is quickly distributed, whilst at the same time controlling air assets and even UAVs.

The capabilities of the Hawkeye were extended yet again in 2003, during Operation Enduring Freedom in Afghanistan. In this theatre Hawkeye’s from the USS Enterprise, operating from Bagram Air Base in Afghanistan, performed the Airborne Battlefield Command, Control and Communications (ABCCC) role in support of ground forces, enabling communications to be maintained in the mountainous terrain, allocating aircraft and helicopters into the battlespace as well as co-coordinating requirements from Forward Air Controllers. In summary, the E-2 Hawkeye has become a combination of a smaller version of a combined E-3 and J-STARS, a capability few would ever have imagined possible and versions of this remarkable aircraft will be around for many years to come.